nothing is wrong of being immature at the age of 16. However, at the age of 30 and beyond, that's when you should start realizing that you should act according to your age. Now is the time to act all immature. Enjoy!

I belonged to the "immature group" in school, we had great fun and messed around every day.

These days that whole group are getting various sorts of education on universities all over europe. While the "cool and mature" people are all in their early 20s and living on wellfare, looking for a job or living of their parents income.... I think the most fortunate one is leading a local junior soccer team.